The following is offered as background information only and is not admitted to be prior art to the present invention.
Cellular signal transduction is a fundamental mechanism whereby external stimuli that regulate diverse cellular processes are relayed to the interior of cells. Growth factor receptors ("Gfrs") are an important part of the signal transduction pathway. Gfrs are cell-surface proteins. When bound by a growth factor ligand, Gfrs are converted to an active form which interacts with proteins on the inner surface of a cell membrane. As the result of this interaction, one of the key biochemical mechanisms of signal transduction is initiated; i.e., the reversible phosphorylation of various proteins within the cell. This phosphorylation of intra-cellular proteins causes the formation inside the cell of complexes with a variety of cytoplasmic signaling molecules that, in turn, effect numerous cellular responses such as cell division (proliferation), cell differentiation, cell growth, expression of metabolic effects to the extracellular microenvironment, etc. For a more complete discussion, see Schlessinger and Ullrich, Neuron, 9:303-391 (1992). See also, Posada and Cooper, Mol. Biol. Cell., 3:583-392 (1992) and Hardie, Symp. Soc. Exp. Biol., 44:241-255 (1990).
The molecules which effect the phosphorylation of proteins are called protein kinases ("PKs"). One of the classes of PKs, which is of particular importance to the present invention, phosphorylates proteins on the alcohol moiety of serine, threonine and tyrosine residues in eukariotic cells. These PKs fall essentially into two groups, those specific for phosphorylating serines and threonines, and those specific for phosphorylating tyrosines. The protein tyrosine kinases ("PTKs") can be further divided into receptor PTKs, abbreviated "receptor tyrosine kinases" or "RTKs" and non-receptor PTKs, sometimes refered to as "cellular tyrosine kinases" or "CTKs."
The RTKs are comprised of an extracellular glycosylated ligand binding domain, a transmembrane domain and an intracellular cytoplasmic catalytic domain that can phosphorylate tyrosine residues on proteins. On the other hand CTKs are entirely intra-cellular and do not contain extracellular and transmembrane domains.
PTKs play an important role in the control of cellular processes including proliferation, differentiation, migration and survival. Enhanced PTK activity due to activating mutations or overexpression has been implicated in many human cancers. It is clear from numerous studies (q.v, infra) that the activity of PTKs must be tightly controlled in normal cells and healthy tissue, as mutations resulting in overactivity of PTKs cause diseases that are associated with excessive cell growth and proliferation while mutations which result in reduction or loss of activity can cause, e.g., embryonal lethality or developmental disorders.
The RTKs comprise one of the larger families of PTKs and have diverse biological activity. At present, at least nineteen (19) distinct subfamilies of RTKs have been identified. One such subfamily is the "HER" family of RTKs, which include EGFR (epithelial growth factor receptor), HER2, HER3 and HER4. These RTKs consist of an extracellular glycosylated ligand binding domain, a transmembrane domain and an intracellular cytoplasmic catalytic domain that can phosphorylate tyrosine residues on proteins. One well-known example of the apparent involvement of PTKs/RTKs in cellular disorders is the association of Her2 over-expression with breast cancer (Slamon, et al., Science, 244:707 (1989).
Another RTK subfamily consists of insulin receptor (IR), insulin-like growth factor I receptor (IGF-1R) and the insulin receptor related receptor (IRR). IR and IGF-1R interact with insulin, IGF-I and IGF-II to form a heterotetramer of two entirely extracellular glycosylated .alpha. subunits and two .beta. subunits which cross the cell membrane and which contain the tyrosine kinase domain.
A third RTK subfamily is referred to as the platelet derived growth factor receptor ("PDGFR") group, which includes PDGFR.alpha., PDGFR.beta., CSFIR, c-kit and c-fms. These receptors consist of glycosylated extracellular domains composed of variable numbers of immunoglobin-like loops and an intracellular domain wherein the tyrosine kinase domains is interrupted by unrelated amino acid sequences.
Another group which, because of its similarity to the PDGFR subfamily, is sometimes subsumed in the later group is the fetus liver kinase ("flk") receptor subfamily. This group is believed to be made of up of kinase insert domain-receptor fetal liver kinase-1 (KDR/FLK-1), flk-1R, flk-4 and fms-like tyrosine kinase 1 (flt-1).
Finally, the FGFR family of PTKs contains at least four distinct members: FGFR1 (also called Flg and Cek1), FGFR2 (also called Bek, Ksam, KsamI and Cek3), FGFR3 (also called Cek2) and FGFR4. They share a common structure consisting of, in the mature protein, one or more immunoglobulin-like (IgG-like) loops flanked by characteristic cysteines, a hydrophobic transmembrane domain and a intracellular domain containing a catalytic region that is split by a short insert; See Ullrich and Schlessinger, Cell, 61:203 (1990).
A more complete listing of the known RTK subfamilies is described in Plowman et al., DN&P, 7(6):334-339 (1994) which is incorporated by reference, including any drawings, as if fully set forth herein.
At present, over 24 CTKs in 11 subfamilies (Src, Frk, Btk, Csk, Abl, Zap70, Fes, Fps, Fak, Jak and Ack) have been identified. The Src subfamily appear so far to be the largest group of CTKs and includes Src, Yes, Fyn, Lyn, Lck, Blk, Hck, Fgr and Yrk. For a more detailed discussion of CTKs, see Bolen, Oncogene, 8:2025-2031 (1993), which is incorporated by reference, including any drawings, as if fully set forth herein.
Both RTKs and CTKs have been implicated in a host of pathogenic conditions including, significantly, cancer.
Other pathogenic conditions to which RTKs and CTKs have been linked include, without limitation, psoriasis, hepatic cirrhosis, diabetes, atherosclerosis, arterial restinosis, kidney sclerosis, wound scarring and a variety of renal disorders.
With regard to cancer, two of the major hypotheses advanced to explain the excessive cellular proliferation that drives tumor development relate to functions known to be PTK regulated. That is, it has been suggested that malignant cell growth results from a breakdown in the mechanisms that control cell division and/or differentiation. It has been shown that the protein products of a number of proto-oncogenes are involved in the signal transduction pathways that regulate cell growth and differentiation. These protein products of proto-oncogenes include the extracellular growth factors, transmembrane growth factor PTK receptors (RTKs) and cytoplasmic PTKs (CTKs), discussed above.
In view of the apparent link between PTK-related cellular activities and a number of virulent human disorders, it is no surprise that a great deal of effort is being expended in an attempt to identify ways to modulate PTK activity. Some of these have involved biomimetic approaches using large molecules patterned on those involved in the actual cellular processes (e.g., mutant ligands (U.S. App. No. 4,966,849)); soluble receptors and antibodies (App. No. WO 94/10202, Kendall and Thomas, Proc. Nat'l Acad. Sci., 90:10705-09 (1994), Kim, et al., Nature, 362:841-844 (1993)); RNA ligands (Jelinek, et al., Biochemistry, 33:10450-56); Takano, et al., Mol. Bio. Cell 4:358A (1993); Kinsella, et al., Exp. Cell Res. 199:56-62 (1992); Wright, et al., J. Cellular Phys., 152:448-57)) and tyrosine kinase inhibitors (WO 94/03427; WO 92/21660; WO 91/15495; WO 94/14808; U.S. Pat. No. 5,330,992; Mariani, et al., Proc. Am. Assoc. Cancer Res., 35:2268 (1994)).
More recently, attempts have been made to identify small molecules which act as PTK inhibitors. For example, bis-monocylic, bicyclic and heterocyclic aryl compounds (PCT WO 92/20642), vinylene-azaindole derivatives (PCT WO 94/14808 and 1-cyclopropyl-4-pyridylquinolones (U.S. Pat. No. 5,330,992) have been described as tyrosine kinase inhibitors. Styryl compounds (U.S. Pat. No. 5,217,999), styryl-substituted pyridyl compounds (U.S. Pat. No. 5,302,606), quinazoline derivatives (EP App. No. 0 566 266 A1), selenaindoles and selenides (PCT WO 94/03427), tricyclic polyhydroxylic compounds (PCT WO 92/21660) and benzylphosphonic acid compounds (PCT WO 91/15495) have all been described as compounds for use as PTK inhibitors for use in treatment of cancer.